The use of aerators are widely used to enhance treatment operations of a sewage waste treatment facility. For example, surface aerators are often employed to treat the surface of a waste water lagoon or basin. Surface aeration does little to enhance the aeration at the lower levels of the lagoon or basin.
There are also a variety of fine bubble aeration devices in which compressed air is discharged at or near the bottom of a waste treatment basin or reservoir. The compressed air (or other gas) is passed through the small pores of a diffuser plate and released as a plurality of fine bubbles. The bubbles, rising to the surface, increase the aeration and dissolve oxygen content of the waste liquid. Frequently, mechanical stirrers are used in conjunction with aerators to increase the physical mixing of the biosolids and to better distribute the dissolved oxygen which results from the aeration equipment.
It is known in the art that the efficiency of aeration equipment for oxygen transfer in water is a function of the air bubble surface area and the time function of the air bubble surface area and the time of contact (residence time) between the bubble and the water. The size of air bubbles directly affects the surface area of the bubble. This particular parameter is controlled by the diffuser design. For any given volume of air, a plurality of small bubbles will provide a greater surface area than a single large bubble.
An additional parameter affecting the bubble size and surface area relates to the volume and flow rate of air. For a typical diffuser, it is a rather simple matter to calculate and determine the optimum air flow rate with a given diffuser which yields the greatest total surface area, and hence, aeration of the water. The residence time between the bubble and the water is also a function of both bubble size and the depth of submergence of the diffuser within the water. A smaller bubble will rise more slowly and increase the residence time. Conversely, a large bubble will rise more quickly but has a shorter residence time and a smaller surface area. In general, the majority of air injected into the water by the diffusers and aeration devices discussed above makes a single vertical pass through the water column before being released at the water's surface. Accordingly, there is room for improvement and variation within the art.